Magnetostrictive sensing technology is a practical tool for the generation and reception of physical elastic guided waves in many common engineering structures. For wave generation, the approach relies on the MS (or Joule) effect which is the manifestation of small changes in the physical dimensions of ferromagnetic materials caused by an externally applied magnetic field. For receiving elastic waves, it relies on the inverse MS (or Villari) effect which is a change in the magnetic induction of a ferromagnetic material caused by a mechanical stress or strain. Since the technology exploits the magnetostriction of materials, it is known as MS sensing.
Early applications of MS sensing relied on the ferromagnetic properties of the material to be inspected which limited its use. Later improvements employed a thin metallic strip of highly MS material which was bonded to the surface of the structure, allowing inspection of nonferrous and nonmetallic objects. These later MS sensing devices continued to suffer from a number of drawbacks, however. They were of fixed size and rigid thus limiting their potential deployment applications or requiring custom manufacture to specific sizes and situations. Additionally, the construction of the sensor is manually intensive requiring hand wrapping of the wire windings. The process involves a skilled technician through all construction steps following precise procedures to limit variability between sensors. Moreover, once the sensor is completed, it is specific to the final sensor profile. For example, a sensor built for a 12 inch diameter pipe cannot be used on a different diameter pipe or as a plate probe.
What is needed, therefore, is an improved manufacturing process using innovative circuit printing techniques that can produce an MS sensor design that is flexible enough to be applied to many different structure geometries.